Applicant is aware of various versions of apparatus for playing games of skill comprising a board or tray having a flat playing surface and a plurality of disc-like playing pieces. The pieces are mounted on the surface such that a region of the surface, as large as at least some of the pieces, is not covered thereby. The object of these games is to slide pieces adjacent the uncovered region of the surface into that region thereby slidably to move the pieces on the surface relative to one another into a predetermined eventual configuration. These games, because of the two-dimensional playing surface, are all constrained to two-dimensional thinking.